Semiconductor device

ABSTRACT

A semiconductor device includes a control section, a first arm, and a second arm; and has an H-bridge circuit to supply an input current supplied from a power source to an output terminal as a reversible electric current on the basis of a control signal outputted from the control section and a reverse-connection-time backflow prevention circuit to prevent an electric current in a direction opposite to the direction of the input current from being supplied to the H-bridge circuit. The first arm is formed over a first island. The second arm is formed over a second island. The control section and the reverse-connection-time backflow prevention circuit are formed over a third island.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2012-242183 filed onNov. 1, 2012 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a semiconductor device to control theforward or reverse rotation of electrical equipment such as a motor.

A motor capable of forward rotation and reverse rotation is used inorder to operate a power window or a door lock of an automobile forexample. A mechanical switch (relay switch) is generally used forcontrolling the forward or reverse rotation of a motor. In recent yearshowever, a forward reverse control circuit using a semiconductor devicehas been used increasingly.

FIG. 1 shows an example of an H-bridge circuit for materializing forwardreverse control with a semiconductor device. A first arm is formed bycoupling a drain of a MOS transistor 104 that is a P-channel MOStransistor of a high side to a drain of a MOS transistor 106 that is anN-channel MOS transistor of a low side. Meanwhile, a second arm isformed by coupling a drain of a MOS transistor 105 that is a P-channelMOS transistor of a high side to a drain of a MOS transistor 107 that isan N-channel MOS transistor of a low side. An H-bridge in which thefirst arm and the second arm are parallelly-coupled is formed bycoupling sources of the high side MOS transistors 104 and 105 to asupply terminal 103 and coupling sources of the low side MOS transistors106 and 107 to an earth terminal 102. A pair of terminals for driving amotor 108 is formed at a middle point node of the first arm and a middlepoint node of the second arm.

When the motor 108 rotates forward, a control circuit turns on the MOStransistors 104 and 107 and turns off the MOS transistors 105 and 106.As a result, electric current flows through the MOS transistor 104, themotor 108, the MOS transistor 107, and then the earth terminal 102 insequence and the motor rotates forward. When the motor rotatesreversely, the control circuit turns on the MOS transistors 105 and 106and turns off the MOS transistors 104 and 107. As a result, electriccurrent flows through the MOS transistor 105, the motor 108, the MOStransistor 106, and then the earth terminal 102 in sequence. On thisoccasion, the electric current flows in the motor 108 in a directionopposite to the direction of the flow in the event of forward rotationand hence the motor 108 rotates reversely.

An example of a semiconductor device for driving a motor is described inJapanese Unexamined Patent Application Publication No. 2007-12857.

SUMMARY

When the forward or reverse flow of electric current is controlled witha semiconductor device shown in FIG. 1, if a power source is coupledreversely, there is the possibility that a large reverse current flowsin an H-bridge circuit through a parasitic diode of a MOS transistor. Atechnology of protecting a semiconductor device against such a situationis desired. Other problems and novel features will appear from thedescription and attached drawings in the specification.

A semiconductor device has a control section and an H-bridge circuit.The H-bridge circuit includes a first arm and a second arm; and suppliesinput current supplied from a power source to a motor 108 as areversible electric current on the basis of a control signal outputtedfrom the control section. The first arm is formed over a first islandand the second arm is formed over a second island. Areverse-connection-time backflow prevention circuit to prevent electriccurrent flowing in a direction opposite to the direction of an inputcurrent from being supplied to the H-bridge circuit is formed over anisland identical to the control section.

Since a reverse-connection-time backflow prevention circuit is formedover an island identical to a control section to control an H-bridgecircuit, it is possible to materialize a configuration of protecting asemiconductor device to control the forward or reverse flow of electriccurrent against reverse connection of a power source by a simplestructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an H-bridge;

FIG. 2 is a circuit diagram of a semiconductor device according to afirst embodiment;

FIG. 3 shows a layout of a semiconductor device according to the firstembodiment;

FIG. 4 is a sectional view of a second island over which a control chipand a reverse-connection-time backflow prevention circuit are mounted;

FIG. 5 shows relationship between a control chip and areverse-connection-time backflow prevention circuit;

FIG. 6 shows a layout of a semiconductor device according to a secondembodiment; and

FIG. 7 shows a layout of a semiconductor device according to a thirdembodiment.

DETAILED DESCRIPTION

Some embodiments are hereunder explained in reference to attacheddrawings. FIG. 2 shows a semiconductor device 1 according to FirstEmbodiment. The semiconductor device 1 has: a control chip 2 having asemiconductor circuit for control; and an H-bridge circuit controlledwith the control chip 2. The H-bridge circuit supplies an input currentsupplied from a power source having a supply terminal Vbat and an earthterminal GND to a motor 108 as a reversible electric current. TheH-bridge circuit has MOS (or MIS) transistors Tr1 to Tr4. Each of Tr1 toTr4 is a power MOSFET used for the application of power electronics suchas the drive current of the motor 108 and a vertical MOSFET having a lowon-resistance is used frequently.

A first arm is formed by coupling a drain of a PMOS transistor Tr1 of ahigh side to a drain of an NMOS transistor Tr3 of a low side at a nodeN3. A second arm is formed by coupling a drain of a PMOS transistor Tr2of the high side to a drain of an NMOS transistor Tr4 of the low side ata node N4. A source of Tr1 and a source of Tr2 are coupled to the supplyterminal at a node N2. A source of Tr3 and a source of Tr4 are coupledto a node N1. As a result, the first arm and the second arm areparallelly-coupled and the H-bridge is formed. The node N3 at the middlepoint of the first arm and the node N4 at the middle point of the secondarm have output terminals respectively and are coupled to the terminalsof both electrodes of the motor 108.

The H-bridge is coupled to a source of a MOS (or MIS) transistor Tr5 ofan N-channel for reverse-connection-time backflow prevention at the nodeN1. A drain of Tr5 is coupled to the earth terminal GND. Tr5 is also avertical MOSFET having a low on-resistance. In a parasitic diode of Tr5,an anode is coupled to the side of a high potential and a cathode iscoupled to the side of an earth electrode. Consequently, if a battery iscoupled reversely when Tr5 is turned off, the parasitic diode of Tr5 iscoupled reversely and the supply of electric current to thesemiconductor device 1 is inhibited.

FIG. 3 shows a layout of the semiconductor device 1. The thin linesconnecting between elements and terminals represent signal wires and thethick lines represent electric current wires through which a relativelylarge electric current flows in power electronics for driving a motorand the like. The semiconductor device 1 has three islands I1 to I3. Thefirst arm, namely the MOS transistors Tr1 and Tr3 having the drainscoupled in common, is formed over the first island I1. The second arm,namely the MOS transistors Tr2 and Tr4 having the drains coupled incommon, is formed over the second island I2. The third island I3 isallocated between the island I1 and the island I2 and the control chip 2and the MOS transistor Tr5 for reverse-connection-time backflowprevention are formed thereover.

Over the first island I1, the source of Tr1 is coupled to the supplyterminal VB of the semiconductor device 1 through an electric currentwire (thick line) and acts as the node N2 in FIG. 2. The drain of Tr1and the drain of Tr3 are coupled in common to a substrate of the islandI1 and act as the node N3. The semiconductor device 1 has a plurality ofterminals formed over a lead frame and the source of Tr3 is coupled to aterminal T1 of the semiconductor device 1 through an electric currentwire.

Over the second island I2, the source of Tr2 is coupled to the supplyterminal VB of the semiconductor device 1 through an electric currentwire (thick line) and acts as the node N2 in FIG. 2. The drain of Tr2and the drain of Tr4 are coupled in common to the substrate of theisland I1 and act as the node N4. The source of Tr4 is coupled to aterminal T4 of the semiconductor device 1 through an electric currentwire.

The source of the MOS transistor Tr5 over the third island I3 is coupledto a terminal T2 and a terminal T3 of the semiconductor device 1 throughelectric current wires. When the semiconductor device 1 having such aconfiguration is mounted over a wiring substrate or the like, theterminal T1 is coupled to the terminal T2 and the terminal T3 is coupledto the terminal T4 through wires L1 and L2 outside the semiconductordevice 1. As a result, the sources of Tr3, Tr4, and Tr5 are coupled incommon at the node N1.

In other words, when the first terminal T1 is electrically coupled tothe second terminal T2 through the external wire L1, the first arm overthe first island I1 is coupled between both the electrodes Vbat and GNDof a power source through Tr5 forming a reverse-connection-time backflowprevention circuit. When the third terminal T3 is electrically coupledto the fourth terminal T4 through the external wire L2, the second armover the second island I2 is coupled between both the electrodes Vbatand GND of the power source through Tr5 forming thereverse-connection-time backflow prevention circuit.

FIG. 4 is a schematic sectional view of a third island I3. A controlchip 2 and a vertical N-channel MOS transistor Tr5 for preventingreverse current are formed over the third island I3. Various types areconsidered as a concrete configuration of Tr5 but, in the example ofFIG. 4, an n⁺ layer 11 is formed over an island I3, an n⁻ layer 12 isformed over the n⁺ layer 11, and a p well 13 and an n⁺ well 15 areformed through a diffusion process applied to the n⁻ layer 12. Afterthose layers are formed, a gate oxide film 18, a gate electrode 17, anda source electrode 16 are formed. The n⁺ layer 11 functions as a drainelectrode. A channel formed in the n⁻ layer 12 is controlled in responseto a voltage applied to the gate electrode 17. In response to thechannel control, electric current of a controlled quantity flows throughthe route ranging from the n⁺ layer 11 on the drain side to the sourceelectrode 16 via the n⁻ layer 12, the p well 13, and the n⁺ well 15. Byforming many such vertical MOS transistors in the island I3, it ispossible to materialize a reverse-connection-time backflow preventioncircuit that: allows a relatively large electric current to flow in aforward direction and a reverse direction with a small on-resistancewhen a channel is formed; and prevents electric current in a reversedirection when a channel is not formed.

The control chip 2 includes a semiconductor circuit having asemiconductor element C-Tr for controlling such as a bipolar transistor,an N-channel MOS transistor, a P-channel MOS transistor, a CMOS circuit,or a DMOS (Double diffusion MOS). Each of those elements generally has ahorizontal MOS or MIS structure in which terminals of a gate, a source,a drain, and the like are formed on the element surface side. The rearside thereof, namely the side of the island I3, is earthed. In FIG. 3,the island I3 is coupled to the earth terminal GND of the semiconductordevice 1.

As shown in FIG. 2, the drain of the MOS transistor Tr5 is coupled tothe earth electrode. Since Tr5 is a vertical NMOS transistor, the rearside (substrate side) acts as a drain. Consequently, as shown in FIG. 5,use of a third island I3 as an earth electrode can form a control chip 2and a MOS transistor Tr5 for reverse-connection-time backflow preventionover the island I3 in common.

That is, in an H-bridge circuit for forward reverse control, it ispossible to materialize a semiconductor device incorporatingreverse-connection-time backflow prevention function by forming a MOStransistor Tr5 for reverse-connection-time backflow prevention over anisland I3 over which a control chip 2 is also formed. Since it isunnecessary to prepare an island dedicated to a reverse-connection-timebackflow prevention circuit, it is possible to obtainreverse-connection-time backflow prevention function by a simpleconfiguration.

In the present embodiment further, since wires L1 and L2 are formedoutside a semiconductor device 1, it is unnecessary to prepare a routefor a relatively large electric current used for driving a motor or thelike among islands I1 to I3. Consequently, it is possible to materializea protection circuit without applying thick wire bonding between islandsthat seldom prevails technologically.

The semiconductor device 1 having such a configuration operates asfollows. Firstly the semiconductor device 1 is mounted over a wiringsubstrate or the like. At the moment, the terminal T1 is coupled to theterminal T2 through the wire L1 and the terminal T3 is coupled to theterminal T4 through the wire L2. When a battery to supply a relativelylarge electric current for mechatronics such as driving the motor 108 isnot coupled to the semiconductor device 1, the MOS transistor Tr5 keepsthe state of being turned off.

When a battery is coupled, the control chip 2 detects the polarity ofthe battery by a preliminarily-arranged detection means. When thepolarity of the battery is detected as normal, the control chip 2 makesthe voltage drop caused by the reverse-connection-time backflowprevention circuit in a low state by turning on the MOS transistor Tr5.Subsequently, the H-bridge circuit operates ordinarily by a signal fromthe control chip 2 and the motor 108 (may also be another mechatronicscomponent) rotates forward or backward.

When the motor 108 rotates forward, the control chip 2 turns off Tr2 andTr3 and turns on Tr1 and Tr4 (driven by PWM or the like). As a result,an input current supplied from the supply terminal VB to the source ofTr1 is outputted from the drain of Tr1 to the output terminal (themiddle point terminal of the first arm) of the first island I1. Theoutput current is supplied to a terminal of the motor 108. The otherterminal of the motor 108 is coupled to the input terminal (the middlepoint terminal of the second arm) of the third island I3. The inputcurrent is inputted from the drain of Tr4, outputted to the source, andfurther outputted to the wire L2. The output current of the wire L2 isinputted into the source of Tr5, outputted to the drain, and outputtedto the earth terminal GND of the third island I3. When the motor 108rotates backward, the control chip 2 turns off Tr1 and Tr4, turns on Tr2and Tr3, and operates in the same manner as the case of forwardrotation.

When plus and minus (Vbat and GND) of the battery are coupled inversely,the MOS transistor Tr5 is turned off and hence reverse current isprevented at Tr5. As a result, it is possible to protect thesemiconductor device 1 when the battery is connected inversely.

FIG. 6 is a plan view showing a layout of a semiconductor device 1 aaccording to Second Embodiment. A coupling method of a node N1 isparticularly different from First Embodiment. In the present embodiment,common connection of sources of Tr3, Tr4, and Tr5 at the node N1 ismaterialized with wires of a lead frame. Specifically, a source of a MOStransistor Tr3 over a first island I1 is coupled to a source of a MOStransistor Tr5 over a third island I3 through a wire L3 formed as a partof the lead frame. Further, a source of a MOS transistor Tr4 over asecond island I2 is coupled to the source of the MOS transistor Tr5 overthe third island I3 through a wire L4 formed as another part of the leadframe. That is, lead frame terminals form a route of an input currentbetween a reverse-connection-time backflow prevention circuit and anH-bridge circuit.

In the present embodiment, a lead frame is shared by a plurality ofislands I1 to I3 and electric current wires are coupled through the leadframe without the segmentation of the lead frame. In comparison withFirst Embodiment, since the wires L3 and L4 for preventing backflow inthe event of reverse connection are installed inside the semiconductordevice 1 a, it is unnecessary to prepare a wire dedicated to areverse-connection-time backflow prevention circuit on the side of amounting board.

FIG. 7 is a plan view showing a layout of a semiconductor device 1 baccording to Third Embodiment. In the present embodiment too, a couplingmethod of a node N1 is particularly different from First Embodiment. Inthe present embodiment, a wire L5 that is an electric current wirebetween Tr3 and Tr5 is materialized with thick bonding wires betweenislands. A wire L6 that is an electric current wire between Tr4 and Tr5is also materialized with thick bonding wires between islands. That is,the bonding wires form a route of an input current between areverse-connection-time backflow prevention circuit and an H-bridgecircuit. If a technology of a thick bonding wire for a large electriccurrent advances, it is expected that such effects as obtained in thepresent embodiment improve.

Although the invention established by the present inventors hasheretofore been explained concretely on the basis of the embodiments, itgoes without saying that the present invention is not limited to theembodiments and can be variously modified in the range not deviatingfrom the tenor of the present invention. For example, it is possible toincorporate the embodiments according to the present invention in anuncontradictory range.

What is claimed is:
 1. A semiconductor device, comprising: a controlsection; an H-bridge circuit comprising a first arm and a second arm andsupplying an input current supplied from a power source to an outputterminal as a reversible electric current on the basis of a controlsignal outputted from the control section; and a reverse-connection-timebackflow prevention circuit to prevent an electric current flowing in adirection opposite to the direction of the input current from beingsupplied to the H-bridge circuit, wherein the first arm is formed over afirst island, wherein the second arm is formed over a second island, andwherein the control section and the reverse-connection-time backflowprevention circuit are formed over a third island.
 2. The semiconductordevice according to claim 1, wherein the reverse-connection-timebackflow prevention circuit is an N-channel vertical power MOSFETelement having a parasitic diode coupled reversely when an electriccurrent is supplied in a direction opposite to the direction of theinput current.
 3. The semiconductor device according to claim 1, whereineach of the first arm and the second arm is formed by coupling a drainof a PMOS of a high side and a drain of an NMOS of a low side in common.4. The semiconductor device according to claim 1, wherein the H-bridgecircuit is coupled to the reverse-connection-time backflow preventioncircuit with an external wire through a terminal prepared in thesemiconductor device.
 5. The semiconductor device according to claim 1,wherein the semiconductor device further has a first terminal coupled tothe first arm, a second terminal and a third terminal coupled to thereverse-connection-time backflow prevention circuit, and a fourthterminal coupled to the second arm, wherein, when the first terminal iselectrically coupled to the second terminal, the first arm is coupledbetween both electrodes of the power source through thereverse-connection-time backflow prevention circuit, and wherein, whenthe third terminal is electrically coupled to the fourth terminal, thesecond arm is coupled between both electrodes of the power sourcethrough the reverse-connection-time backflow prevention circuit.
 6. Thesemiconductor device according to claim 1, wherein the semiconductordevice further has lead frame terminals coupled to thereverse-connection-time backflow prevention circuit and the H-bridgecircuit, and wherein the lead frame terminals form a route of the inputcurrent between the reverse-connection-time backflow prevention circuitand the H-bridge circuit.
 7. The semiconductor device according to claim1, wherein the semiconductor device further has bonding wires to couplethe reverse-connection-time backflow prevention circuit to the H-bridgecircuit, and wherein the bonding wires form a route of the input currentbetween the reverse-connection-time backflow prevention circuit and theH-bridge circuit.